The present disclosure relates to a vent apparatus for regulating discharge of fuel vapor from a fuel tank, and particularly to an apparatus for venting fuel vapor laden with hydrocarbon material from the vapor space in a fuel tank to a charcoal canister. More particularly, the present disclosure relates to a refueling ventilation and fill-limit system for controlling tank ventilation and for preventing overfilling of a fuel tank.
Vehicle fuel systems include valves associated with a fuel tank and configured to vent pressurized or displaced fuel vapor from the fuel tank to a vapor recovery canister located outside the fuel tank. The canister is designed to capture and store hydrocarbons entrained in fuel vapors that are vented in the fuel tank. Pressurized fuel vapor is discharged from the fuel tank to the canister during a typical vehicle refueling operation. Later, hydrocarbons are purged from the canister and burned in a vehicle engine.
Fill-limit vent valves are coupled to fuel tanks and configured to “open” and vent fuel vapor from a vapor space in a fuel tank to a canister during early stages of refueling but “close” to stop further venting when the tank is full. Closure of the fill-limit vent valve blocks flow of fuel vapor to the canister. This causes fuel vapor pressure to increase in the fuel tank vapor space to displace liquid fuel extant in the fuel tank causing some of that displaced liquid fuel to flow out of the fuel tank and into the filler neck. The displaced fuel moves upwardly in the filler neck in a direction toward a fuel-dispensing pump nozzle arranged to extend into the mouth of the filler neck. The upwardly moving liquid fuel reaches the nozzle and actuates a shut-off mechanism or sensor associated with the pump nozzle. Pump nozzles are known to include a fill-limiting sensor and a shut-off mechanism coupled to the sensor and configured to shut off the flow of fuel from the nozzle into a fuel tank filler neck whenever the tank is full and liquid fuel “backs up” the filler neck to splash onto or reach the fill-limiting sensor located on the nozzle.